Chromium, tungsten cobalt base alloys containing additions of tantalum, titanium and niobium



D 1965 J. J. RAUSCH ETAL 3,223,522

CHROMIUM, TUNGSTEN COBALT BASE ALLOYS CONTAINING ADDITIONS OF TANTALUM, TITANIUM AND NIOBIUM Filed Jan. 51, 1965 5 Sheets-Sheet 1 uTs, KSI

STRENGTH AT I700F.

O l I I I l lo RA DUCTILITY AT I700 F.

DUGTILITY AT 30- ROOM TEMPERATURE IO-- U W 0 1 C0 l5Gr 5 IO I5 20 ALLOY ADDITION. WT. le

R EFFECT OF ADDITION ON THE PROPERTIES INVENTO 5 OF THE BASE COMPOSITION Co-l5Cr. JOHNJ RAUSGH JOSEPH 8. Mc ANDREW BY 9: ATTORNEY FIG. I

1965 J. J. RAUSCH ETAL 3,223,522

CHROMIUM, TUNGSTEN COBALT BASE ALLOYS CONTAINING ADDITIONS OF TANTALUM, TITANIUM AND NIOBIUM Filed Jan. 31, 1963 6 Sheets-Sheet 2 UTS, KSI

lo R A DUCTILITY AT [700 F.

o l I I DUGTILITY AT ROOM TEMPERATURE /u RA 0 I I Co-200r 5 IO I5 ALLOY ADDITION, WT. /o

EFFECT OF ADDITION ON THE PROPERTIES OF THE BASE COMPOSITION CO'ZOCf.

FIG. 2

Dec. 14, 1965 J. RAUSCH ETAL 3,223,522

, TUNGSTEN COBALT BASE ALLOYS CONTAININ CHROMIUM ADDITIONS OF TANTALUM, TITANIUM AND NIOBIUM 1963 5 Sheets-Sheet 5 Filed Jan. 31,

0 O O O O 0 0O Co-l5 Cr TERNARY ADDITION WT. "/9

United States Patent CHRSMIUM, TUNGSTEN COBALT BASE ALLOYS CONTATNING ADDITIONS 0F TANTALUM, Tl- TANTUM AND NIOBIUM John J. Rausch, Evanston, and Joseph B. McAndrew, Chicago, 111., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Jan. 31, 1963, Ser. No. 255,415 2 Claims. (Cl. 75-171) The present invention relates to improved cobalt alloys and to methods of making the same. More particularly, the present invention relates to the addition of predetermined amounts of various selected materials to cobalt and cobalt-base alloys whereby alloys having markedly improved physical and metallurgical properties are obtained.

The present commercial cobalt alloys do not provide the strengths demanded by modern high-temperature applications in highly oxidative atmospheres. Attempts to produce alloys of cobalt embodying these desirable properties have heretofore not been successful due to a loss in forgeability or in extensive brittleness on additional alloying.

Accordingly, it is an object of the present invention to provide an alloy of cobalt that is strong and ductile while retaining sufficient forgeability to be workable after additional alloying.

A further object of the present invention is to provide an oxidation resistant alloy of cobalt that embodies the aforementioned properties.

Yet another object of the present invention is the provision of cobalt alloys that exhibit significant increases in rupture life, are oxidation resistant, and display short time tensile strength in the range of 60,000 to 85,000 p.s.i. at 1700 F.

Yet another object of the present invention is to provide novel, wrought cobalt-base alloys that are superior in properties to those presently used for high-temperature applications.

Still another object of the present invention is the provision of alloys of cobalt having a 1000 hour rupture life at 10,000 psi. and 1700 F.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying tables and graphs wherein:

FIG. 1 is a graphical presentation of the efl'ect of tungsten addition on the properties of the base composition Co-lSCr;

FIG. 2 is a graphical presentation of the eifect of tungsten addition on the properties of the base composition Co-20Cr; and

FIG. 3 is a graphical presentation of the effect of tungsten addition on the 1700 F. short-time yield strength of Co-Cr base alloys.

The above objects are accomplished by the preparation of alloys of the desired properties. Initially basic ternary alloys of cobalt, chromium and tungsten were prepared which exhibited good tensile strength, forgeability, ductility, and oxidation resistance. These ternary alloys were adopted among others as the basis for the search for an alloy of cobalt having improved stress rupture life while not sacrificing any of the properties of the parent alloy.

The stress rupture properties are improved primarily through dispersion strengthening. For this purpose small additions of at least one metal from the group consisting of titanium, tantalum and columbium is made.

The composition limits within which forgeability is maintained in binary cobalt-chromium alloys have been established. These alloys may be alloyed to the solubility limit (-38 w/o Cr) before loss of forgeability occurs. The addition of 20% or more chromium to cobalt produces alloys having excellent strength at 1700 F. The yield strength of these alloys rises continuously from 18,000 psi. at 20% Cr to 43,500 p.s.i. to 35% Cr.

It has been found that alloys based on Co-Cr are strengthened appreciably at 1700 F. by the addition of tungsten. The effect is illustrated in FIGS. 1, 2 and 3. These alloys have the following properties.

TABLE I Tensile properties of ternary cobalt base alloys at room temperature Alloy Yield Ultimate Elong. Ex. Addition Strength Tensile Percent (percent (wt. (p.s.i.) Strength RA in 0.625 percent) (p.s.i.) in.)

1 r-10W 90,500 157,000 25 17 116, 000 164, 000 21 23 97, 000 149, 000 17 16 78, 000 148,000 30 37 141, 000 175, 000 13 13 6 25Cr-10W 95,000 160,000 33 36 At 1,700 F.

Yield Ultimate Elong. Ex. Strength Tensile Percent (percent (p.s.i.) Strength RA in 0.625

(p.s.i.) in.)

Significant quantities of tungsten can be added to cobalt at the 15 and 20 w/o levels without causing embrittlement at room temperature or 1700 F.

Based on this ternary alloy containing 15 to 35% chromium, 5 to 20% tungsten, balance cobalt, additional alloying elements were investigated to obtain maximum stress rupture properties. Selective additions of titanium, niobium and tantalum accomplished these objectives. The addition of titanium or niobium to the Co-Cr base alloys should be restricted to about 1 to 2% to minimize loss of forgeability. However, tantalum may be added in percentages of 2 to 4% to the ternary Co-Cr-W alloy or to the quaternary alloy containing titanium or niobium or combinations thereof. The stress rupture properties of the ternary base alloy and the alloys containing the additional elements is shown in Table II.

It is now apparent that the novel alloys of the present invention display an unusual and valuable combination The significant increases in strength obtained by the small addition of reactive metals is probably due to reaction with interstitial elements in the base alloy, i.e. through dispersion strengthening.

The most notable improvement in rupture life occurred in alloys based on. Co-Cr-20W. Addition of 1% Cb, 2% Ta or 1% Ti caused a to 175 fold increase in rupture life at 1700 F. and under astress of 10,000 p.s.i. In each instance more uniform elongation was noted than occurred in the base alloy.

The alloy Co-15Cr-20W-1Ti had a rupture life of 922 hours at 10,000 p.s.i. and 1700 F. compared to approximately 100 hours under these conditions for one of the better commercial wrought alloys. The stress to rupture is about higher at this temperature for the alloys of this invention.

Alloys were prepared as 250-gram pancake-shaped ingots approximately /2 inch X 3 inch diameter. These ingots were are melted using a water-cooled, tungstentipped electrode in a water-cooled copper crucible in an argon atmosphere. The ingots were then hammer forged to /2 inch diameter rod from which test specimens were prepared. Two dilferent heat treatments were employed, consisting of a stabilizing anneal after forging or a solution treatment followed by a stabilizing anneal. The latter invariably resulted in superior rupture life.

Tensile tests were performed at room temperature and at 1700 F. at a strain of approximately 0.12 inch/inch/ minute. Before testing, all specimens were sealed in evacuated bulbs, treated at 1700 F. for 24 hours, and then air cooled.

of properties making them useful for various critically needed applications in the jet engine and aero-space fields.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a forgeable, oxidation resistant alloy consisting of 45-80% cobalt, 15-35% chromium, 5-20% tungsten, the addition of 2-4% tantalum and 1-2%- titanium. char acterized by a 30-170 fold increase in rupture life at 1700 F. and under a stress of 10,000 p.s.i.

2. In a forgeable, oxidation resistant alloy consisting of 45-80% cobalt, 15-35% chromium, 520% tungsten, the addition of 2-4% tantalum and 12% niobium characterized by a 30-170 fold increase in rupture life at 1700 F. and under a stress of 10,000 p.s.i.

References Cited by theExamiuer UNITED STATES PATENTS 2,974,036 3/1961 Thielemann 171 2,974,037 3/1961 Thielemann 75171 2,996,379 8/1961 Faulkner 75-171 3,026,199 3/ 1962 Thielemann 75-171 3,085,005 4/1963 Michael et al. 75171 3,118,763 1/1964 Thielemann 75-170 DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner. 

1. IN A FORGEABLE, OXIDATION RESISTANT ALLOY CONSISTING OF 45-80% COBALT, 15-35% CHROMIUM, 5-20% TUNGSTEN, THE ADDITION OF 2-4% TANTALUM AND 1-2% TITANIUM CHARACTERIZED BY A 30-170 FOLD INCREASE IN RUPUTRE LIFE AT 1700*F. AND UNDER A STRES OF 10,000 P.S.I. 